Signal transmission from a starting point to a receiver, having a substantially higher voltage potential, for example, occurs within a transmitter if there is a high-voltage between the control grid of a power tube and the starting point of the signal transmission. In this case, a point of separation, for example an isolating transformer between the starting point and the receiver, whose potentials have a high differential, must be provided in the transmission path to the control grid which, in this case, forms a receiver.
Difficulties occur with breakdowns in the isolating transformers, due to the fact that as a result intolerably high voltage are produced at its terminals. Furthermore, with other types of breakdown, voltages are coupled between the isolating transformer coils so that undesirable interference voltages are produced at its terminals.
Even if interfering voltages could be limited by means of semi-conductor-produced voltage peak limitations, there would still be a residual undesirably high interfering voltage.